Analysis of a resistance force for the locked-wheel of push-pull locomotion rovers using large subsidence

This paper provides a quantitative analysis of the resistance force of the locked-wheel for push-pull locomotion rovers using intentional sinkage. Our previous study has confirmed that push-pull locomotion using intentional subsidence at an initial position can contribute to improving the traveling performance. The key factor of this scheme is the resistance force of the locked-wheel. However, the resistance force at different sinkage conditions and wheel sizes (e.g., mass, width, and diameter) remains unclear, especially for the individual locked-wheel. The detailed investigation of this interaction can contribute to the accurate estimation of rover mobility. This paper, therefore, investigates the locked-wheel and soil interaction at different sinkage conditions experimentally, especially focusing on the intentional sinkage condition. Additionally, the resistance force is considered theoretically through the knowledge based on the soil flow patterns beneath the locked-wheel. The experimental results confirmed that the resistance force of the locked-wheel rose as the initial sinkage, wheel size, and weight increases. Furthermore, the theoretical calculation suggested the resistance force increased with a similar tendency of the experimental data.     

Monotone strain-stress models for shape memory alloys hysteresis loop and pseudoelastic behaviorx

To describe the behavior of Shape Memory Alloy we use a thermomechanical model, founded on a free energy which is a convex function with respect to the strain and to the martensitic volume fraction, and a concave one with respect to the temperature. The material parameters of the model are experimentally determined.Received: November 26, 2001; revised: March 20, 2002     

Some Primitive Concepts in Continuum Mechanics Regarded in Terms of Objective Space-Time Molecular Averaging: The Key Rôle Played by Inertial Observers

In Continuum Mechanics the notions of body, material point, and motion, are primitive. Here these concepts are derived for any (possibly time-dependent) material system via mass and momentum densities whose values are local spacetime averages of molecular quantities. The averaging procedure necessary to ensure molecular-based densities can be agreed upon by all observers (that is, are objective) has implications for constitutive relations. Specifically, such relations should first be expressed in terms of Galilean-invariant functions of the motion relative to an inertial frame. Thereafter such relations can be re-phrased for general observers, thereby yielding general-frame constitutive relations compatible with material frame-indifference. Two postulates concerning observer agreement (which together constitute a statement of material frame-indifference) are shown to imply that any stress response function which is assumed to depend upon the motion in an inertial (general) frame must be Galilean-invariant (invariant under superposed rigid body motions). Accordingly, invariance under superposed rigid body motions is not a fundamental tenet of continuum physics, but rather a consequence of material frame-indifference whenever constitutive dependence upon motion in a general observer frame is postulated.     

Synthesis of mesoporous silica nanosphere using different templates

Synthesis of mesoporous silica nanosphere were carried out using polyvinyl pyrrolidine and different templates with surfactant property, namely cetyltrimethylammonium bromide, cetyltrimethylammonium chloride, n-octylamine, tetrapropylammonium bromide (TPABr) and these amines give good yield except TPABr. Attempts with other amines without surfactant properties, such as n-propylamine, diethylamine, triethylamine, triethanolamine templates did not give any precipitate in the present reaction scheme. The above synthesis followed by sonication did not change the trend. However addition of dodeycl sodium sulfate surfactant before sonication gave precipitate in all amines, which shows particle growth is induced by surfactant.     

A novel MC DS-CDMA system scheme with high spectral efficiency

1 Introduction Recently, some studies [1, 2] have shown that the Multi- Carrier code-division multiple-access (CDMA) systems can exhibit excellent performance in beyond 3G or 4G mobile communication systems. In general, multicarrier (MC) CDMA systems have…     

A bifurcation-based decohesion model for simulating the transition from localization to decohesion with the MPM

Based on recent experimental observations on the formation of localization before delamination, a bifurcation-based decohesion approach is proposed in this paper to simulate the transition from localization to decohesion involved in the delamination process of compressed films. The onset and orientation of discontinuous failure are identified from the discontinuous bifurcation analysis. A discrete constitutive model is then formulated based on the bifurcation analysis to predict the evolution of material failure as decohesion or separation of continuum. The Material Point Method, that does not employ fixed mesh-connectivity, is developed as a robust spatial discretization method to accommodate the multi-scale discontinuities involved in the film delamination. To demonstrate the potential of the proposed approach, a parametric study is conducted to explore the effects of aspect ratio and failure mode on the evolution of failure patterns under different boundary conditions, which provides a better understanding on the physics behind the film delamination process.Received: January 16, 2003; revised: August 11, 2003     

Effective elastic moduli and stress concentrator factors in random structure aligned fiber composites

We consider a linearly elastic composite medium, which consists of a homogeneous matrix containing a statistically uniform random set of aligned fibers. Effective elastic moduli as well as the stress concentrator factors in the components are estimated. The micromechanical approach is based on the Green’s function technique as well as on the generalization of the “multiparticle effective field method” (MEFM, see for references, Buryachenko [1]). The refined version of the MEFM takes into account the variation of the effective fields acting on each pair of fibers. The dependence of effective elastic moduli and stress concentrator factors on the radial distribution function of the fiber locations is analyzed. Received: October 20, 2004     

Weak solutions of the interior boundary value problems of plane Cosserat elasticity

In this paper we formulate interior Dirichlet and Neumann boundary value problems of plane Cosserat elasticity in Sobolev spaces, show that these problems are well-posed and find the corresponding weak solutions in the form of integral potentials. Received: April 7, 2005     

基于导频的OFDM信道估计

从最小二乘和最小均方误差两种估计准则出发，结合OFDM多载波并行传输中符号时间长度大于信道冲散响应持续时间的特点，在块状和梳状导频图案下。导出了时域和频域的信道估计算法。最后采用广义平稳非相关散射假设下的多径时变瑞利衰落信道模型。对各个算法进行了仿真,比较了不同导频图案下备算法对系统误符号率的影响，分析结果表明。当导频数大于以采样间隔为量度的等效信道长度时。时域估计比频域估计精度更高;当导频数目小于等效长度时,最小均方估计优于最小二乘估计。     

Superconducting properties of rapidly quenched and heat treated Zr-V and Hf-V foils

The results of rapid quenching and subsequent heat treatments on the superconducting properties of the Zr-V and Hf-V binary systems are presented. Metallic glasses can be prepared in these systems which have very attractive properties for practical application. The existence of a flexible glassy phase raises the prospect of alternative methods for the construction of superconducting devices. As-quenched, partially crystalline material is characterized by small critical currents, yet relatively large upper critical fields and transition temperatures. Heat treatments considerably enhance the current carrying capability. Work supported by Department of Energy Contract No. DE-AC03-76ER00822.